1. Field of the Invention
The present invention relates to a position indicator, such as a stylus pen, a coordinate input device equipped with the position indicator, and a variable capacitor used as a pen pressure detecting section in the position indicator.
2. Description of the Related Art
In recent years, a coordinate input device has been used as an input device of, for example, a personal computer. Such a coordinate input device includes a pen-like position indicator and a position detecting device having an input surface, on which input operation such as pointing operation, handwritten character input operation or hand-drawn illustration input operation is performed using the position indicator.
A variable capacitor such as disclosed in Japanese Unexamined Patent Application Publication No. H04-96212 generally corresponding to U.S. Pat. No. 5,206,785, incorporated by reference herein, is used as a pen pressure detecting section of the position indicator. The variable capacitor includes a first electrode attached on one surface of a dielectric, and a second electrode. The second electrode is a flexible member arranged facing the other surface of the dielectric. The variable capacitor is provided with a member for spacing the second electrode and the other surface of the dielectric from each other, except for certain portions thereof, by a very small distance, and a member for applying a pressure to the second electrode towards the dielectric.
FIGS. 34A and 34B show a concrete configuration of a variable capacitor 200 disclosed in Japanese Unexamined Patent Application Publication No. H04-96212. The variable capacitor 200 includes a substantially disc-like dielectric 201, a first electrode 202 attached on one surface 201a of the dielectric 201, and a second electrode 203 arranged on the side of the other surface 201b of the dielectric 201. The second electrode 203 is a flexible member disposed on the side of the other surface 201b of the dielectric 201 via a ring-shaped spacer 204. Further, a rod 210 is disposed on the side of the second electrode 203 opposite to the dielectric 201 via an elastic body 205.
A first terminal 206 is disposed on the side of one surface of the first electrode 202. The first terminal 206 includes a disc-like flange portion 206a and a lead portion 206b. The lead portion 206b extends from substantially the center of one surface of the flange portion 206a in the direction opposite to the dielectric 201. When a pen pressure is applied, the flange portion 206a contacts the one surface of the first electrode 202 so as to be electrically connected to the first electrode 202.
A second terminal 207 is arranged on an end (or edge) portion of the second electrode 203. Similar to the first terminal 206, the second terminal 207 is configured by a disc-like flange portion 207a and a lead portion 207b. The lead portion 207b extends from substantially the center of one surface of the flange portion 207a along the side of the dielectric 201. When a pen pressure is applied, the flange portion 207a contacts an end (or edge) portion of one surface of the second electrode 203 so as to be electrically connected to the second electrode 203.
The spacer 204 is interposed between the other surface 201b of the dielectric 201 and the second electrode 203. In a state where no pressure is applied to the rod 210 (i.e., when the variable capacitor is in an initial state), a very small space is formed between the other surface 201b and the second electrode 203 of the variable capacitor 200. When a pressure is applied to the rod 210, as shown in FIG. 34B, the second electrode 203 will contact the other surface 201b of the dielectric 201. When a further higher pressure is applied to the rod 210, the contact area between the second electrode 203 and the other surface 201b of the dielectric 201 will increase, and therefore the capacitance value between the first terminal 206 and the second terminal 207 will increase. The pressure (i.e., pen pressure) applied to the rod 210 is detected by detecting the variation of the capacitance value between the first terminal 206 and the second terminal 207.